JP6403389B2 - Method for producing imide-based porous film and imide-based porous film - Google Patents

Description

The present invention relates to a method for producing an imide-based porous film having excellent heat resistance and good permeability, and an imide-based porous film.

Imide porous films are used in the fields of industrial materials such as lithium secondary battery separators, filters, and separation membranes, medical materials, optical materials, and electronic materials because of their excellent heat resistance. ing. As a method for producing this imide-based porous film, an imide-based polymer solution containing a good solvent and a poor solvent as a solvent is applied onto a substrate to form a coating film, which is then dried in a drying furnace. Thus, there is known a method for obtaining an imide-based porous film (hereinafter, this method may be abbreviated as “dry-type porous process”). (Patent Documents 1 to 3)

The dry porous process is different from the wet porous process in which a coating film formed on a substrate is immersed in a coagulating liquid containing a poor solvent to make the porous film when producing an imide-based porous film. It is not necessary to use a coagulation bath for making the pores. Therefore, when an imide-based porous film is produced industrially, no waste liquid is generated from the coagulation bath, and this is an excellent method with good environmental compatibility.

Japanese Patent No. 4947899 JP2013-64122A JP 2013-216776 A

However, when the imide-based porous film obtained by a known dry porous process is applied to a separator or filter for a lithium secondary battery, a separation membrane, etc., permeability to liquids and gases required for these (hereinafter, In some cases, it was simply abbreviated as “permeability”.

Therefore, the present invention solves the above-mentioned problems, and provides a method for producing an imide-based porous film having excellent heat resistance and good permeability, and an imide-based porous film obtained by this method. With the goal.

The present inventors have found that the above-mentioned problems can be solved by performing drying under specific conditions when drying the coating film in the dry porous process, and the present invention has been completed.

The present invention has the following objects.
<1> An imide polymer solution containing a good solvent and a poor solvent as a solvent is applied onto a substrate to form a coating film, and is dried in a drying furnace to thereby obtain an imide porous film. In the drying process, the solvent evaporating from the coating film surface is sprinkled in the space in the drying furnace and heated by any one of the following methods 1) to 3). A method for producing an imide-based porous film.
1 ) Circulate the solvent exhausted from the drying furnace.
2 ) After providing a spacer at the end of the coating film surface, a solvent vapor permeable coating material is laminated and heated through this spacer.
3 ) A solvent vapor permeable coating material is directly laminated on the coating surface.
<2> The imide-based porous material according to <1> , wherein the poor solvent is at least one selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol, and triethylene glycol. Quality film manufacturing method.
<3> An imide polymer solution containing a good solvent as a solvent and a poor solvent selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol, and triethylene glycol. Is coated on a substrate to form a coating film, and this is heated in the drying furnace while increasing the solvent vapor pressure near the coating film surface in the atmosphere in the drying furnace to obtain an imide-based porous film. On the surface, 5 μL of a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 1: 1: 1) set at 30 ° C. was dropped, and the time until this completely penetrated was dropped. Imido porous film that is 150 seconds or less The use of the lithium secondary battery separator, filter or separation membranes.

According to the production method of the present invention, an imide-based porous film can be easily obtained by a simple process. The obtained imide-based porous film has excellent heat resistance and good permeability.

2 is a SEM image of a cross section of an imide-based porous film of Example 2. 3 is a SEM image of the surface of an imide-based porous film in Example 2. 4 is a SEM image of the surface of an imide-based porous film of Comparative Example 2. It is a schematic diagram which shows the drying method of a coating film.

Hereinafter, the present invention will be described in detail.
The present invention relates to a method for producing an imide-based porous film and an imide-based porous film obtained by this production method.

Here, the imide-based polymer forming the imide-based porous film is a polymer having an imide bond in the main chain or a precursor thereof. Typical examples of the polymer having an imide bond in the main chain include polyimide, polyamideimide, and polyesterimide. However, it is not limited to these.

Among imide polymers, for example, polyimide and polyamideimide can be preferably used. As the polyimide, a precursor type polyimide using polyamic acid as a precursor (applied to a polyimide that is insoluble in a solvent when used as a polyimide) or a soluble type polyimide (soluble in a solvent as a polyimide) can be used. Among these imide polymers, aromatic polyimides and aromatic polyamideimides excellent in mechanical properties and heat resistance are preferable. The aromatic polyimide or aromatic polyamideimide may be thermoplastic or non-thermoplastic. Of these, aromatic polyimide or aromatic polyamideimide having a glass transition temperature of 200 ° C. or higher can be preferably used.

In the method for producing an imide-based porous film of the present invention, first, a solution of the imide-based polymer (hereinafter sometimes abbreviated as “imide-based coating solution”) is used as a solution for coating on a substrate. prepare. As a solvent for this imide coating solution, a mixed solvent of a poor solvent and a good solvent is used. In this way, when the coating film is dried and solidified, phase separation occurs due to the action of the poor solvent remaining in the coating film, and the imide polymer that is a solute has a porous structure. it can. Here, the good solvent means a solvent having a solubility in an imide polymer of 1% by mass or more at 25 ° C., and the poor solvent means a solvent having a solubility in an imide polymer of less than 1% by mass at 25 ° C. Say. The poor solvent preferably has a boiling point higher than that of the good solvent, and the difference in boiling points is preferably 5 ° C or higher, more preferably 20 ° C or higher, and further preferably 50 ° C or higher.

As the good solvent, an amide solvent is preferably used. Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP boiling point: 202 ° C.), N, N-dimethylformamide (DMF boiling point: 153 ° C.), N, N-dimethylacetamide (DMAc boiling point: 166 ° C.). Is mentioned. These may be used alone or in combination of two or more. As the poor solvent, an ether solvent is preferably used. Examples of ether solvents include diethylene glycol dimethyl ether (boiling point: 162 ° C), triethylene glycol dimethyl ether (boiling point: 216 ° C), tetraethylene glycol dimethyl ether (boiling point: 275 ° C), diethylene glycol (boiling point: 244 ° C), triethylene glycol. And a solvent such as (boiling point: 287 ° C.). These may be used alone or in combination of two or more. However, as described above, there is no limitation as long as the solvent has a boiling point of 5 ° C. or higher than that of the good solvent and can be a poor solvent for the imide polymer. The blending amount of the poor solvent is preferably 40 to 90% by mass and more preferably 60 to 80% by mass with respect to the total amount of the solvent.

Examples of imide-based coating solutions such as polyamic acid solution, soluble polyimide solution, polyamideimide solution, etc., are trade names “Uimide varnish BP” (polyamic acid type polyimide solution) commercially available for porous formation from Unitika Ltd. , Trade name “U imide varnish SP” (soluble polyimide solution), trade name “U imide varnish IP” (polyamide imide solution) and the like. In these coating liquids, a mixed solvent of an amide solvent and an ether solvent is used as a solvent.

Although the above-mentioned commercially available product may be used as the imide-based coating liquid composed of the polyimide precursor polyamic acid solution and the soluble polyimide solution, the raw material tetracarboxylic dianhydride and diamine are mixed in approximately equimolar amounts. In addition, a polyamic acid solution or a soluble polyimide solution obtained by subjecting it to a polymerization reaction in the mixed solvent described above is also preferably used. In addition, after a polymerization reaction only in a good solvent to obtain a solution, a method of adding a poor solvent thereto, or after a polymerization reaction only in a poor solvent to obtain a suspension, a method of adding a good solvent thereto. Thus, an imide-based coating liquid can also be obtained.

Examples of the tetracarboxylic dianhydride include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 3,3 ′, 4,4'-diphenylsulfone tetracarboxylic acid, 3,3 ', 4,4'-diphenyl ether tetracarboxylic acid, 2,3,3', 4'-benzophenone tetracarboxylic acid, 2,3,6,7-naphthalene Tetracarboxylic acid, 1,4,5,7-naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 3,3 ', 4,4'-diphenylmethanetetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,4,9,10-tetracarboxype Dianhydrides such as len, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane Is used. These may be used alone or in combination of two or more. Among these, pyromellitic acid and 3,3 ′, 4,4′-biphenyltetracarboxylic acid are preferable.

Examples of the diamine include p-phenylenediamine, m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 3,3'-dimethyl-4,4. '-Diaminodiphenylmethane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,2-bis (anilino) ethane, diaminodiphenylsulfone, diaminobenzanilide, diaminobenzoate, diaminodiphenyl sulfide, 2, 2-bis (p-aminophenyl) propane, 2,2-bis (p-aminophenyl) hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4-bis (p-amino) Phenoxy) benzene, , 4'-bis (p-aminophenoxy) biphenyl, diaminoanthraquinone, 4,4'-bis (3-aminophenoxyphenyl) diphenyl sulfone, 1,3-bis (anilino) hexafluoropropane, 1,4-bis ( Anilino) octafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino) tetradecafluoroheptane is used. These may be used alone or in combination of two or more. Among these, p-phenylenediamine, 4,4′-diaminodiphenyl ether, and 2,2-bis [4- (4-aminophenoxy) phenyl] propane are preferable.

1-50 mass% is preferable and, as for the solid content density | concentration of the polyamic acid in a polyimide precursor solution, 5-25 mass% is more preferable. The polyamic acid contained in the polyimide precursor solution may be partially imidized. The viscosity at 30 ° C. of the polyimide precursor solution is preferably 1 to 150 Pa · s, and more preferably 5 to 100 Pa · s.

In order to obtain the polyamideimide solution of the present invention, commercially available products as described above may be used. However, the trimellitic acid component (trimellitic anhydride chloride, trimellitic anhydride, etc.) and the diamine component (various diamines) as raw materials are used. Alternatively, a solution obtained by blending the diisocyanate derivative) in an approximately equimolar amount and subjecting it to a polymerization reaction in the mixed solvent can also be preferably used. In addition, after obtaining a solution by polymerization reaction only in a good solvent, a method of adding an ether solvent to this, or after obtaining a suspension by polymerization reaction only in a poor solvent, an amide solvent is added thereto. The polyamideimide solution can also be obtained by the addition method.

As the trimellitic acid component as a raw material, trimellitic anhydride chloride is preferable. Alternatively, a trimellitic acid component partially substituted with a component such as pyromellitic acid, benzophenonetetracarboxylic acid, biphenyltetracarboxylic acid, or terephthalic acid may be used.

Examples of the diamine component include m-phenylenediamine, p-phenylenediamine, 4,4′-diphenylmethanediamine, 4,4′-diphenyletherdiamine, diphenylsulfone-4,4′-diamine, and diphenyl-4,4′-. Diamine, o-tolidine, 2,4-tolylenediamine, 2,6-tolylenediamine, xylylenediamine, naphthalenediamine or their diisocyanate derivatives can be used. These may be used alone or in combination of two or more. Among these, 4,4′-diphenyl ether diamine and m-phenylene diamine are preferable.

1-50 mass% is preferable and, as for the solid content density | concentration of the polyamide-imide in a polyamide-imide solution, 10-30 mass% is more preferable. The polyamideimide solution has a viscosity at 30 ° C. of preferably 1 to 150 Pa · s, and more preferably 5 to 100 Pa · s.

If necessary, known additives such as various surfactants and organic silane coupling agents may be added to the imide-based coating liquid as long as the effects of the present invention are not impaired. Moreover, you may add other polymers other than an imide type polymer to the imide-type coating liquid in the range which does not impair the effect of this invention as needed.

In the method for producing an imide-based porous film of the present invention, the imide-based coating solution is applied to the surface of a substrate, dried at 100 to 150 ° C., and then heat-treated at 250 to 350 ° C. as necessary. Thus, an imide-based porous film having a porosity of 30 to 90% by volume can be formed. Thereafter, the porous imide-based film can be peeled from these substrates to form a porous imide-based film alone. Moreover, the imide-type porous film shape | molded on the base material can also be laminated and integrated with a base material, and can be used. In this process, the porosity and pore diameter can be adjusted by selecting the type and amount of the solvent (good solvent and poor solvent) in the imide coating solution.

Examples of the substrate include metal foil, metal wire, glass plate, plastic film, various woven fabrics, various non-woven fabrics, etc., and gold, silver, copper, platinum, aluminum and the like can be used as the metal. . These may be porous or non-porous. As a method of applying the coating liquid to the substrate, a dip coater, a bar coater, a spin coater, a die coater, a spray coater, or the like can be used, and the coating can be applied continuously or batchwise.

In the method for producing an imide-based porous film of the present invention, at the time of the drying, it is essential to heat the solvent while increasing the solvent vapor pressure in the vicinity of the coating film surface in the drying furnace to dry the coating film. It is. As a result, a large number of pores are formed on the surface of the coating film, and the surface porosity increases, so that an imide-based porous film with good permeability can be obtained. The quality of the permeability can be determined from, for example, the permeation time of a solvent when a specific solvent (for example, a solvent for an electrolyte solution constituting a lithium ion secondary battery) is dropped on the surface of the imide-based porous film. it can. Details of the determination method will be described later. In the imide-based porous film of the present invention, the permeation time is preferably 300 seconds or shorter, and more preferably 150 seconds or shorter.

In order to heat while increasing the solvent concentration remaining in the coating film and the solvent vapor pressure in the vicinity of the coating film surface in the atmosphere in the drying furnace, for example, (1) (2) By circulating the solvent exhausted from the drying furnace, the solvent evaporating from the coating film surface can be dispersed in the space in the drying furnace and heated. . Such a method is a preferable method when the coating is continuously performed. In addition, when the application is performed in a batch system, as shown in FIG. 4, after providing a spacer at the end of the coating surface, a solvent vapor permeable coating material (for example, a commercially available porous material) A film or a non-woven fabric) may be laminated and heated, or the coating material may be laminated directly on the coating film surface, and the evaporated solvent may be spread over the coating film surface. In this case, the solvent vapor pressure can be adjusted by selecting the solvent vapor permeability of the covering material and the thickness of the spacer. When performing by a batch type, the method performed using such a coating | covering material is preferable.

The porosity of the imide-based porous film obtained by the production method is preferably 30 to 90% by volume, more preferably 40 to 85% by volume, and more preferably 45 to 80% by volume. preferable. By setting the porosity in this way, good mechanical properties and permeability can be ensured at the same time. The porosity of the imide-based porous film is a value calculated from the apparent density of the imide-based porous film and the true density (specific gravity) of the imide-based polymer constituting the imide-based porous film. Specifically, the porosity (volume%) is calculated by the following formula when the apparent density of the imide-based porous film is A (g / cm ³ ) and the true density of the imide-based polymer is B (g / cm ³ ). Calculated.
Porosity (volume%) = 100−A * (100 / B)

The average pore diameter of the imide porous layer is preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm. By setting the average pore diameter in this way, good permeability can be ensured. 1-100 micrometers is preferable and, as for the thickness of an imide type porous film, 10-50 micrometers is more preferable.

As described above, since the method for producing an imide-based porous film of the present invention is based on a dry-type porous process, waste liquid from a coagulation bath containing a poor solvent is not generated during pore formation. Therefore, the environmental compatibility is good and the process is very simple. Since the obtained imide-based porous film is excellent in permeability, it can be suitably used as a separator for a lithium secondary battery, a filter, a separation membrane or the like.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples.

<Example 1>
A Uimide varnish BP (polyamic acid type polyimide solution) manufactured by Unitika Co., Ltd. was prepared as a coating solution, and this was coated on a 30 cm square aluminum plate, and then a spacer having a thickness of 2 mm and a width of 2 cm was provided on four sides of the aluminum plate. . Through this spacer, the entire coating film on the aluminum plate was coated with a commercially available fluororesin porous film having a thickness of 30 μm and an average pore diameter of 0.5 μm. This was put into a hot air circulation type drying furnace set at 130 ° C., heated for 30 minutes, further heated at 300 ° C. for 60 minutes, then cooled and peeled from the aluminum plate to obtain a porosity of 55 μm and a porosity of Obtained a porous film (A-1) comprising 58% by volume of polyimide. The permeability of the obtained porous film was evaluated by the following method. That is, 5 μL of a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 1: 1: 1) set at 30 ° C. was dropped on the film surface, and it was visually observed that this completely penetrated. The penetration time was measured and the permeability was evaluated according to the criteria in Table 1.
Table 2 shows the results of evaluating the permeability of the porous film (A-1).

<Example 2>
A porous film (A-2) was prepared and evaluated in the same manner as in Example 1 except that the spacer thickness was 0.5 mm.
Moreover, the cross-section of this film and the SEM image of the surface are shown in FIGS. From these figures, it can be seen that continuous pores having an average pore diameter of about 3 μm are formed. It can also be seen that many pores having an average pore diameter of about 3 μm are formed on the surface. The pores formed on the surface contribute to the good permeability of the porous film (A-2).

<Example 3>
A porous film (A-3) was prepared in the same manner as in Example 1 except that the average pore size of the fluororesin porous film was 0.2 μm, and the evaluation results are shown in Table 2.

<Example 4>
Unitika Co., Ltd. U imide varnish IP (polyamideimide solution) was prepared as a coating solution, and this was coated on a 30 cm square aluminum plate, and then a spacer having a thickness of 2 mm and a width of 2 cm was provided on four sides of the aluminum plate. Through this spacer, the entire coating film on the aluminum plate was coated with a commercially available fluororesin porous film having a thickness of 30 μm and an average pore diameter of 0.5 μm. This is put into a hot-air circulating drying oven set at 130 ° C., heated for 30 minutes, then cooled and peeled from the aluminum plate, thereby comprising a polyamideimide having a thickness of 30 μm and a porosity of 55% by volume. A porous film (A-4) was obtained. Table 2 shows the results of evaluation in the same manner as in Example 1.

<Example 5>
A porous film (A-5) was prepared and evaluated in the same manner as in Example 4 except that the thickness of the spacer was 0.5 mm.

<Example 6>
A porous film (A-6) was prepared in the same manner as in Example 4 except that the average pore diameter of the fluororesin porous film was 0.2 μm, and the evaluation results are shown in Table 2.

<Comparative Example 1>
A porous film (B-1) was prepared and evaluated in the same manner as in Example 1 except that the thickness of the spacer was 50 mm.

<Comparative Example 2>
A porous film (B-2) was prepared and evaluated in the same manner as in Example 1 except that the spacer was not used. Moreover, although the SEM image of the surface of this film is shown in FIG. 3, although a pore is recognized slightly on the surface, it turns out that it is a thing with a low porosity.

<Comparative Example 3>

A porous film (B-3) was prepared in the same manner as in Example 4 except that no spacer was used, and the evaluation results are shown in Table 2.

As shown in the Examples, the solvent infiltration time of the porous imide film obtained by the production method of the present invention was as fast as 300 seconds or less. Such good permeability is contributed by a large number of pores formed on the film surface. This surface pore formation is the effect of heating while increasing the solvent vapor pressure in the vicinity of the coating film surface. By increasing the solvent vapor pressure, the poor solvent concentration on the coating film surface increases and surface pore formation This is thought to be due to the promotion of phase separation that contributes to the above.
On the other hand, the solvent permeation time of the porous imide film obtained by the production method shown in the comparative example was delayed to over 300 seconds. This is due to the low hole area on the film surface.

The imide-based porous film that is easily obtained by the production method of the present invention based on the dry porosification process has good permeability and should be suitably used in lithium secondary battery separators, filters, separation membranes, and the like. Can do.

1 Base material 2 Coating liquid 3 Coating material 4 Spacer

Claims (3)

An imide-based porous film is produced by applying a imide polymer solution containing a good solvent and a poor solvent as a solvent on a substrate to form a coating film and drying it in a drying furnace. An imide-based porous material characterized in that, during drying, the solvent evaporating from the surface of the coating film is dispersed in a space in the drying furnace and heated by any one of the following methods 1) to 3): Quality film manufacturing method.
1 ) Circulate the solvent exhausted from the drying furnace.
2 ) After providing a spacer at the end of the coating film surface, a solvent vapor permeable coating material is laminated and heated through this spacer.
3 ) A solvent vapor permeable coating material is directly laminated on the coating surface. The imide-based porous film according to claim 1 , wherein the poor solvent is at least one selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol, and triethylene glycol . Production method. An imide polymer solution containing a good solvent as a solvent and a poor solvent that is at least one selected from the group consisting of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol, and triethylene glycol , It is an imide-based porous film obtained by coating on a material to form a coating film, and heating and drying this while increasing the solvent vapor pressure in the vicinity of the coating film surface in the atmosphere in the drying furnace. Then, 5 μL of a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 1: 1: 1) set at 30 ° C. is dropped on the surface, and the time until this completely penetrates is 150 seconds or less. Of the imide-based porous film Um secondary battery separator, use of the filter or separator membranes.